Home SCIENCE The strongest evidence for a Universe before the Big Bang | by Ethan Siegel | Starts With A Bang! | Oct, 2025

The strongest evidence for a Universe before the Big Bang | by Ethan Siegel | Starts With A Bang! | Oct, 2025

by NORTH CAROLINA DIGITAL NEWS


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When the entire sky is viewed in a variety of wavelengths, certain sources corresponding to distant objects beyond our galaxy are revealed. This first all-sky map from Planck includes not only the cosmic microwave background, but also extragalactic contributions and the foreground contributions from matter within the Milky Way itself. All of these must be understood to tease out the appropriate temperature and polarization signals. (Credit: ESA, HFI and LFI consortia, 2010; CO map from T. Dame et al., 2001)

The hot Big Bang is often touted as the beginning of the Universe. But there’s one piece of evidence we can’t ignore that shows otherwise.

The notion of the Big Bang goes back nearly 100 years, when the first evidence for the expanding Universe appeared. If the Universe is expanding and cooling today, that implies a past that was smaller, denser, and hotter. In our imaginations, we can extrapolate back to arbitrarily small sizes, high densities, and hot temperatures: all the way to a singularity, where all of the Universe’s matter and energy was condensed in a single point. For many decades, these two notions of the Big Bang — of the hot dense state that describes the early Universe and the initial singularity — were inseparable.

But beginning in the 1970s, scientists started identifying some puzzles surrounding the Big Bang, noting several properties of the Universe that weren’t explainable within the context of these two notions simultaneously. When cosmic inflation was first put forth and developed in the early 1980s, it separated the two definitions of the Big Bang, proposing that the early hot, dense state never achieved these singular conditions, but rather that a new, inflationary state preceded it. There really was a…



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